Conventionally, when light is amplified, not only is amplification performed simply, but attenuation is also adjusted for each optical signal to control gain and output, for example. For such adjustment, for example, an optics element (brancher) such as a branch coupler that extracts a portion of an optical signal is used. Further, an attenuator that can adjust the optical attenuation of the light of the optical signal is used. For an example of such a technique, refer to Japanese Laid-Open Patent Publication No. 2006-49405.
Nonetheless, with the conventional techniques above, a problem arises in that to measure the power of output light, a portion of the output light has to be removed and attenuation cannot be efficiently controlled. In cases where the fiber is a multicore fiber, portions of the light are removed (extracted) from plural adjacent locations and thus, the degree of freedom of the extraction diminishes, making the above problem more remarkable.
To solve the problem above related to the conventional techniques, one object of the present invention is to provide an optical device capable of efficiently controlling attenuation.